Duplex system of telephony



June 11, 1929. A Z 1,716,908

DUPLEX SYSTEM OF TELEPHONY Filed Feb. 8, 1927 INVENTOR PAUL TATZ M/L QM/w g A ORNEY Patented June 11, 1929.

UNITED STATES PATENT OFFICE.

PAUL TATZ, OF BERLIN, GERMANY, ASSIGNOR T0 GESELLSCHAFT FUR DRAHTLOSE TELEGRAPHIE M. B. 3., OF BERLIN, GERMANY, A CORPORATION OF GERMANY.

DUPLEX SYSTEM OF TELEPHONY.

Application filed February 8, 1927, Serial No. 166,634, and in- Germany February 26, 1926.

The thing involved in most cases of radio frequency telephony in connection with electricity generating stations is to establish telephonic communication between several stations by way of the existent high-potential air-line system. For economical reasons, arrangements are then so made that for telephonic inter-communication of all stations, the same wave is utilized. Hence, for duplex operation; and this is what is mostly required; there thus results the necessity of using a pair of \VtlYGS common to all of the stations. If the problem is extended so as to include also the demand that each of the stations shall be able to call any one or all of the others, this results in the necessity of changing the wave, here particularly the crossing of sending and receiving wave. By crossing I mean transmitting a signal at one frequency and simultaneously receiving another signal at another frequency.

For reasons of safety, the high frequency connections must be so chosen that dangerous potentials are unable to pass from the airline circuits to the low-potential circuits of the high frequency equipment, the air-line circuit comprising first the air-line itself and further also the connection between the latter and the high frequency equipment, for instance, by way of coupling condensers. This problem is resolved by coupling the transmitter and receiver apparatus with the air-line circuit by way of secondary circuits insuring the required safety against potentials. Hence, if the wave is to be altered in high frequency equipment, that is, if in this special case sending and receiving waves are to be crossed, not only the coupled secondary circuits, but also the air-line circuit itself would have to'be changed. However, for reasons of safety the relays provided to change the connections of the air-line circuit would have to be so designed as to be able to handle the high potentials possibly arising in such a case. Hence, relays of special construction would have to be used.

Now, thepresent invention has as its particular object to dispense with the use of such relays entirely, indeed, its fundamental feature is to make all circuit changes in the air-line circuit unnecessary.

Of course, the problem could be solved by dispensing with the tuning of the coupling for the carrier frequencies that are used. \Vhat is meant here by tuning is the phase compensation of the coupling capacity by the impedance of the high frequency equipment for the carrier frequencies. This would result in lower efliciency with greater chances of disturbances by change in connections in the connected stations.

For this reason, it is advisable to tune the coupling. Maximum receiving effect will always be obtained if the coupling line, by tuning, is given the character of the wave resistance (natural impedance). In order to insure optimum receiving effects under all conditions, such tuning must be effected for both waves comprised in the pair used, simultaneously.

According to the invention, the two-wave character is provided for the coupling line, for the purposes of duplex communication from the very outset, so that in case of wavecrossing no circuit changes in the air-line circuit will be required any longer. The degree of coupling between the coupling line and the secondary receiver and transmitter oscillation circuits is kept sufficiently small so that the double-wave character will not be disturbed, while. on the other hand, it must be kept sufiiciently high in order to secure optimum efliciency.

For the object of two-wave tuning of the coupling line, there are, fundamentally speaking. two different ways and means.

According to one scheme, frequency separation is resorted to by the provision of a circuit branching so that in one circuit or branch only one fre uency, and in the second branch the other frequency is allowed 'to pass, whereupon for wave-crossing, transmitter and receiver can be coupled with the two branches by way of a secondary oscillation circuit in a manner allowing of changeover. This arrangement at the same time offers the advantage that disturbances of the receiver by high amplitudes of the transmit ter frequency in the same station are pre eluded.

In the accompanying drawing Figure 1 shows a circuit arrangement by way of example a'nd adapted to the foregoing scheme.

Figure? is a modified circuit arrangementwhere the'branching cooperates solely with the receiver and,

Figure 3 is still another modified circuit arrangement for transn'iitting and receiving.

Referring to Figure 1 C denotes the highpotential condensers by Way of which the high frequency equipment is joined with the air-line F The two circuit branches first contain stoppers S191 and SpQ for the respective carrier frequencies. Of course, these stoppers can also be built according to the principle of resonance transformers. The valve of their impedance for the frequency to be passed is compensated in proper phase relationship by supplementary impedances Z and Z respectively. The self-inductance coils K and K allow the tuning of the cou pling forthe two frequencies. The supplementary iinpedances Z, of course, if so desired, could be combined with the tuning inductances K. The secondary oscillation circuits coordinated to the receiver or the t ansmitter are coupled with the coils K. They are arranged so as to be changed over, that is to say, transmission and reception apparatus can be connected either to circuit S or circuit S Figure 2 shows a modified form of a circuit arrangement wherein the branching is coordinated only to the receiver, and which at the same time fulfills the object of two-wave tuning of the high-potential condensers C and the transmitter coupling coil. Receiver E on wave crossing is connected either with branch K or K whereas the secondary circuit of the transmitter S is changed in its wave upon wave crossing.

Another method of two-wave tuning of the coupling comprises the addition of impedances in series with the coupling which are given diiferent values for the two frequencies, to be more precise, just the values that are required in order to insure double-wave tuning for the coupling condensers. Figure 3 shows by way of example a circuit arrangement where Z is the additional impedance of two-wave character. L8 and Le the coupling coils for transmitter and receiver are denoted by S and E, respectively. In case of wave transposition (crossing), the secondary cir cuits S and'E must be changed in wave.

. So far as the additional impedance of twowave nature is concerned, various connections are conceivable which are well known. Either there are used two circuit branches being each impermeable to the respective carrier frequency or else there is used a transformer with a secondary circuit coupled therewith.

In case of two-wave tuning comprising the use of an additional impedance, the transmitter, receiver, and additional impedance within the coupling means are connected in series. For this reason, special selecting means must, be used with the receiver apparatus -whereby disturbing actions by the transmitter current upon the receiver will be precluded. Arrangements of this nature (uncoupling devices) which, in the last analysis involve the use of multiple-circuit connections with or without bridge or differential methods, shall not be discussed here because they fall outside the scope of this invention.

I claim as my invention:

1. In a multiplex communicating system utilizing high potential power lines, a circuit arrangement adapted for the simultaneous reception and transmission of signals comprising condensers connected to the power lines for coupling transmission and receiving apparatus thereto and for preventing the application of high potentials to said transmission and receiving apparatus, a branched circuit, each branch of which being adapted for selectively passing a difierent band of frequencies, between said condensers, a receiver adapted to be coupled alternately to each of said branches, and means for coupling a transmitter between one of said condensers and said branched circuit.

2. In a multiplex communicating system utilizing high potential power lines, a circuit arrangement adapted for the simultaneous reception and transmission of signals comprising condensers connected to said power lines,

a branched circuit between said condensers,

each branch of which being adapted for se lectively passing a different band of frequencies, means for coupling radio signalling apparatus alternately to either of said branches, and means for coupling other radio signalling apparatus between said branched circuit and one of said condensers.

PAUL TKTZ. 

